This project consists of studies on the hormonal and behavioral basis of maternal behavior in the rat, the neural site at which maternal behavior is organized and where hormones act in stimulating the onset of maternal behavior, and the ontogeny of maternal behavior. Additional factors being studied are the olfactory basis of maternal behavior, and the factors which contribute to the decline of maternal behavior. Our studies, thus far indicate that prepartum rise in estrogen stimulates the onset of maternal behavior but after maternal behavior is established, pup-stimulation maintains it and causes it to decline eventually. Olfactory stimuli from pups play an important role at first in inhibiting maternal behavior and later in supporting it. The medial preoptic area has proved crucial for maternal behavior and estrogen implanted at this site stimulates short latency maternal behavior while lesions at this site, prevent the appearance of maternal behavior. Maternal behavior appears early in ontogeny, shortly after weaning and undergoes changes with puberty in both females and males. BIBLIOGRAPHIC REFERENCES: Rosenblatt, J.S. 1975 Selective retrieving by maternal and nonmaternal rats. Journal of comparative and physiological Psychology, 88, 678-686. Rosenblatt, J.S. & Siegel, H.I. 1975 Hysterectomy-induced maternal behavior in the rat. Journal of comparative and physiological Psychology, 89, 685-700.